Research objectives of this study are to compare the effects of increasing left atrial pressure in normal dogs with the effects of equal increases in dogs with complete cardiac denervation. Experimental variables to be measured include hemodynamics, renal function, and plasma levels of vasopressin concentration and renin activity. We also propose to do a series of "localizing" experiments, in which we will partially obstruct the circulation at different sites within the thorax. This will be done in an effort to establish whether the hemodynamic and renal effects of certain cardiopulmonary receptors differ from that of other receptors in nearby regions.